Changes in Salivary Analytes of Horses Due to Circadian Rhythm and Season: A Pilot Study.
Authors: Contreras-Aguilar María D, Lamy Elsa, Escribano Damián, Cerón Jose J, Tecles Fernando, Quiles Alberto J, Hevia María L
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary: Salivary Biomarkers and Temporal Variation in Horses Non-invasive salivary sampling offers valuable diagnostic potential for equine practitioners, yet the interpretation of results depends critically on understanding how biological rhythms affect measured analytes. Researchers measured twelve salivary biomarkers related to stress and metabolic function in five healthy mares at two-hourly intervals from 06:30 to 20:30 across two seasons (winter and spring), examining both daily and seasonal patterns. Cortisol, total esterase, butyrylcholinesterase, adenosine deaminase, and creatine kinase exhibited distinct circadian rhythms, with cortisol and several enzyme activities also showing significant seasonal variation and different daily patterns between seasons; alpha-amylase, lipase, and butyrylcholinesterase additionally differed significantly between winter and spring measurements. These findings underscore that sampling time and season substantially influence salivary biomarker values, meaning clinicians must standardise collection protocols and consider temporal context when interpreting results for stress assessment or metabolic screening. Practitioners should establish consistent collection times within their practice and recognise that winter and spring reference ranges may require adjustment, particularly for enzymes and stress markers, to avoid misinterpreting normal physiological variation as pathology.
Read the full abstract on PubMed
Practical Takeaways
- •Salivary cortisol and enzyme levels (TEA, BChE, ADA, CK) in horses vary predictably throughout the day and across seasons; sample timing must be standardized for valid biomarker interpretation
- •Seasonal differences in some analytes (sAA, Lip, BChE) mean reference ranges may need to be season-specific for accurate clinical assessment
- •When using saliva samples for stress or disease biomarkers in horses, document both time of collection and season to avoid misinterpretation of results
Key Findings
- •Cortisol, TEA, BChE, ADA, and CK demonstrated circadian rhythmic patterns in horse saliva across the sampling day
- •sAA, Lip, and BChE showed significantly different values between winter and spring seasons
- •Cortisol, TEA, BChE, and ADA displayed different daily rhythmic patterns depending on season
- •Time of day and season are critical variables for accurate interpretation of salivary analyte measurements in horses